Qt 4.5: Fine-Tuning Features in Qt

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# Fine-Tuning Features in Qt

In many cases, only a fixed set of applications are deployed on an embedded device, making it possible to save resources by minimizing the size of the associated libraries. The Qt installation can easily be optimized by avoiding to compile in the features that are not required.

- Simple Customization

- Embedded Linux
- Windows CE

- Managing Large Numbers of Features

A wide range of features are defined, covering classes and technologies provided by several of Qt's modules. You can look up the different feature definitions in the `src/corelib/global/qfeatures.txt` file within the Qt source distribution.

### Simple Customization

#### Embedded Linux

To disable a particular feature, just run the `configure` script for Qt for Embedded Linux with the `-no-feature-<feature>` option. For example:

     ./configure -no-feature-thread

The feature can easily be enabled again by running `configure` with the `-feature-<feature>` option.

See also Qt Performance Tuning.

#### Windows CE

To disable a particular feature, just run the `configure` script with the set of required `-D<feature>` options. For example, you can use the `-D` option to define `QT_NO_THREAD`:

     configure.exe -D QT_NO_THREAD

The `-D` option only creates a Qt internal define. If you get linker errors you have to define `QT_NO_THREAD` also for your project. You can do this by adding `DEFINES` += `QT_NO_THREAD` to your `.pro` file.

See also Qt Performance Tuning.

### Managing Large Numbers of Features

If you want to disable a lot of features, it is more comfortable to use the `qconfig` tool. You can disable a set of features by creating a custom configuration file that defines the preferred subset of Qt's functionality. Such a file uses macros to disable the unwanted features, and can be created manually or by using the `qconfig` tool located in the `tools/qconfig` directory of the Qt source distribution.

Note: The `qconfig` tool is intended to be built against Qt on desktop platforms.

Windows CE: The Qt for Windows CE package contains a `qconfig` executable that you can run on a Windows desktop to configure the build.

The `qconfig` tool's interface displays all of Qt's functionality, and allows the user to both disable and enable features. The user can open and edit any custom configuration file located in the `src/corelib/global` directory. When creating a custom configuration file manually, a description of the currently available Qt features can be found in the `src/corelib/global/qfeatures.txt` file.

Note that some features depend on others; disabling any feature will automatically disable all features depending on it. The feature dependencies can be explored using the `qconfig` tool, but they are also described in the `src/corelib/global/qfeatures.h` file.

To be able to apply the custom configuration, it must be saved in a file called `qconfig-myfile.h` in the `src/corelib/global` directory. Then use the `configure` tool's `-qconfig` option and pass the configuration's file name without the `qconfig-` prefix and `.h` extension, as argument. The following examples show how this is invoked on each of the embedded platforms for a file called `qconfig-myfile.h`:

Embedded Linux:

     ./configure -qconfig myfile

Windows CE:

     configure.exe -qconfig myfile

Qt provides several ready-made custom configuration files, defining minimal, small, medium and large installations, respectively. These files are located in the `/src/corelib/global` directory in the Qt source distribution.